Impractical individual that is hosting 500 top celebrities (8)

I believe the answer is:

idealist

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'impractical individual' is the definition.
'idealist' can be an answer for 'individual' (idealist is a kind of individual). I am unsure of the 'impractical' bit.

'that is hosting 500 top celebrities' is the wordplay.
'that is' becomes 'ie' (abbreviation for id est, 'that is' in Latin).
'hosting' is an insertion indicator (inserted letters are welcomed in or hosted).
'500' becomes 'D' (Roman numeral for 500).
'top celebrities' becomes 'alist' (the A-list means very famous people).
'ie' enclosing 'd' is 'ide'.
'ide'+'alist'='IDEALIST'

Can you help me to learn more?

(Other definitions for idealist that I've seen before include "philosopher" , "One seeking perfection" , "Seeker after perfection" , "Perfectionist" , "Dreamer" .)

I've seen this clue in The Times.

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